Methyl esters are the building blocks for various compositions ranging from lubricants, polymers, solvents, cosmetics and the like. Branched alkyl esters offer a number of useful features due to their chain length and random branching. More specifically, they are useful as surfactants, oxidatively stable, have low crystallinity, and have a lower melt point than straight chain alkyl esters.
Long, straight chain saturated alkyl esters (C10:0 and higher) are solid at room temperature, which makes them difficult to process in a number of applications. Unsaturated long chain alkyl esters, however, are liquid at room temperature, so are easy to process, but are unstable because of the existence of double bond(s). Branched alkyl esters mimic the properties of the straight chain unsaturated alkyl esters in many respects, but do not have the disadvantage of being unstable. “Branched alkyl esters” means alkyl esters containing one or more alkyl side groups which are attached to the carbon chain backbone at any position. Therefore, branched alkyl esters are for many applications more desirable than straight chain alkyl esters. Commercial branched alkyl esters are not, however, naturally occurring materials.
A number of process are known for the production of branched methyl esters. For example, in the process of U.S. Pat. No. 5,856,539 an alkyl ester feed comprising unsaturated alkyl esters is contacted with a catalyst, characterized in that the catalyst comprises a material having a microporous structure.
U.S. Pat. No. 5,677,473 describes a process for preparing branched chain fatty acids or alkyl esters thereof which comprises subjecting unsaturated fatty acids having 10-25 carbon atoms or alkyl esters thereof to a skeletal isomerization reaction in the presence of water or a lower alcohol using a zeolite as a catalyst. The zeolite has a linear pore structure of a size small enough to retard dimerization and large enough to allow diffusion of the branched fatty acids or alkyl esters thereof.
U.S. Pat. No. 5,364,949 describes a process for the production of branched fatty acids and their esters which comprises reacting unsaturated fatty acids or esters thereof with aliphatic nonactivated olefins in the presence of layer silicates and active carbon.
However, all of these processes are plagued by low yield and/or a high rate of undesireable byproduct formation. Accordingly, there is a need for a new process that overcomes these disadvantages, i.e. a process for the preparation of branched alkyl esters from straight chain unsaturated alkyl ester feedstocks with a high conversion rate, an increased selectivity towards branched monomeric isomers and which employs a reusable catalyst.